1. Field of the Invention
The invention relates to an adjustable mount assembly in which two optical components can be adjusted in relation to each other very precisely, translationally in an x-y plane perpendicular to an axis of rotation and rotationally about said axis of rotation, which is advantageously the common optical axis of the two optical components. Such a mount can be used in particular for mounting so-called spatial filters, in which a micro lens array and an aperture diaphragm array arranged one behind the other have to be oriented so as to be adjusted in relation to each other.
2. Description of the Background Art
U.S. Pat. No. 6,876,494 B2 discloses a device with which light is projected onto a wafer in a predefined structural pattern, by the light being modulated spatially via micro optical components. For the quality of the modulation, amongst other things, the highly accurate adjustment of a micro lens array belonging to the device with respect to an aperture diaphragm array corresponding thereto, which is arranged after the micro lens array in the direction of the optical axis of the micro lens array, is of importance. The optical axis of the micro lens array is understood to be a central axis from the multiplicity of individual optical axes of the individual lenses of the micro lens array.
The device disclosed in U.S. Pat. No. 6,876,494 B2 is based on a prior art, described in JP 2001-21830, according to which, in a generically equivalent device, an aperture diaphragm array is positioned in relation to a micro lens array. It is explained that the micro lens array used in JP 2001-21830 comprises micro lenses having a small numerical aperture and a focal length of 5 mm, for which reason exact positioning in the direction of the optical axis is not to be the subject matter of these considerations. If, however, use is made of a micro lens array with micro lenses of a large numerical perture and a focal length of approximately 250-300 μm, then highly accurate positioning of the aperture diaphragm array in the direction of the optical axis in relation to the micro lens array is necessary, so that the individual components of the light focused by the micro lenses are focused in the aperture diaphragms.
In order to position the micro lens array and the aperture diaphragm array at an exactly predefined distance in relation to each other, according to U.S. Pat. No. 6,876,494 B2 it is proposed to form on the micro lens array or on the aperture diaphragm array at least one projection toward the other array, which projection has a predefined height in the direction of the optical axis and determines the distance between the arrays. Thus, the relative position of the arrays in relation to each other in the direction of the optical axis can be set accurately.
Instead of the at least one projection, a spacer having a predefined thickness can also be inserted between the micro lens array and the aperture diaphragm array.
In relation to the necessity for accurate positioning, also perpendicular to the optical axis (following adjustment in one plane), no information can be gathered from U.S. Pat. No. 6,876,494 B2.
The adjustment in one plane is necessary in order to bring the individual optical axes of the individual lenses of the micro lens array into coincidence with the axes of symmetry of the apertures of the aperture diaphragm array. For the purpose of adjustment in one plane, a relative movement is necessary which has both translational components (travels) in an x-y plane perpendicular to the optical axis and a rotational component (angle) about the optical axis, the travels and angles being only tiny.
Such adjusting movements of the two arrays in relation to each other are afflicted by friction in the event of moderate contact over formed projections or a spacer and are therefore afflicted by stick-slip, which makes a precise, deterministic adjustment in an order of magnitude of 0.05 μm, as is intended by the applicant, very difficult.
Adjustable mounts for optical components, which permit an adjustment in a plane perpendicular to the optical axis of an optical system, generally comprise an outer mount part, which is firmly connected to the housing of the optical system or is a constituent part of the housing, and an inner mount part, which carries the optical component and can be displaced and rotated in relation to the outer mount part in the plane by means of actuating elements.
Adjustable mounts are known in which the mount parts are individual parts which, following the adjustment, have to be fixed in relation to each other, and those in which the mounts are produced monolithically and the mount parts remain in the adjusted position in a self-locking manner without these having to be fixed.
As a rule, the first-named type of mounts is used for relatively large adjustment travels with lower precision, and the second-named type of mounts is used for small actuating travels with high precision.
DE 44 00 869 C1 discloses an adjustable mount (called a device for the lateral adjustment of lenses within a high-power objective there), in which the mount parts are individual parts. The mount comprises an inner mount part (called a lens mount there) and an outer mount part (called a first mount there), which are connected to each other via a detachable clamping device acting axially in a force-fitting manner.
The inner mount part, in which the lens is held, is held within the outer mount part, which can be fitted into an objective housing, by pressing forces which act exclusively parallel to the optical axis of the objective, and which, during an adjustment in a plane perpendicular to the optical axis, are partly compensated for by opposing forces, generated by piezo translators arranged in the inner mount part, so that a displacement of the inner mount part within the outer mount part is possible with action of little radial force.
The outer mount part has an inner planar face, on which the inner mount part is placed by pressure means. Advantageously, the pressure means used is a contact ring firmly connected to the outer mount part, a spring ring and an adjustment ring which is placed on the inner mount. The pressing force of the pressure means, determined by the dimensions of the adjustment ring, and also the spring force of the spring ring, is dimensioned such that the inner mount part is reliably held in its position even under mechanical loadings, e.g. during transport. As a result of the exclusive action of axial forces when fixing the inner mount ring, the possible misalignment thereof during fixing is intended to be avoided.
The opposing force acting during adjustment, produced by the piezo translators, is lower than the pressing force, so that the inner mount part is still always placed on the inner planar face by axial forces and cannot slip in the outer mount part in an undefined manner. A displacement is carried out only with action of a radial force via radially acting actuating elements. Which actuating elements are used has a substantial influence on the reproducibility of the adjustment, the precision thereof, the possible actuating travel and the user friendliness.
The arrangement of four actuating elements offset by 90° in relation to one another is advantageous. Since, in the device according to DE 44 00 869 C1, the actuating elements are not assigned any holding function and the axial pressing force to be overcome during the adjustment is low, the use of piezo translators as actuating elements proves to be particularly advantageous.
DE 10 2008 029 161 B3 discloses a monolithic mount for a lens. It comprises an annular disk, which is subdivided by slots into an inner and an outer mount part, which remain connected to one another, preferably at three points. The remaining connections, the geometric shape and size of which can in principle be implemented differently by means of the position and shape of the slots, determines the possible actuating travel and the precision of the adjustment. According to DE 10 2008 029 161 B3, the connections are formed by toggle levers which is formed of two links which, at one end, are connected to each other via a solid body joint and enclose an angle greater than 90° and less than 180° with each other, and the other ends of which are connected to the outer and the inner mount part, respectively, via solid body joints.
The solid body joints are tapered portions formed by the shape and arrangement of the slots.
As a result of the action of force on the connections (also manipulator units), the inner mount part can be displaced and rotated with respect to the outer mount part within one plane. Monolithic mounts having manipulator units implemented in other ways are known, for example from EP 1 577 693 A2 and DE 10 2007 030 579 A1. The geometry of the manipulator units (shape and dimensioning) determines the possible adjustment travel and the precision of the adjustment.
A device according to DE 10 2008 029 161 B3 is not suitable to adjust two optical components, forming an assembly, in relation to each other and to adjust the assembly in relation to a reference base, e.g. the optical axis of an optical system.
An adjustable mount in which two optical components, forming an optical assembly, can be adjusted very precisely in relation to each other over a large adjustment range and the assembly can be adjusted in relation to a reference base is described in the patent application DE 10 2010 035 223.3 (not yet published), which originates from the applicant.
The mount assembly claimed here comprises an outer mount part and an inner mount part, which together form a first adjustable mount. The outer and the inner mount part each comprise an outer and an inner mount frame, which are each connected to each other monolithically via at least three manipulator units, comprising solid body joints and actuating elements, e.g. actuating screws. They each constitute a second and a third adjustable mount. Fixed in the two inner mount parts in each case is an optical component, which can be adjusted in relation to each other within the mount assembly and jointly in relation to a reference base, specifically the outer mount frame of the outer mount part, by the actuation of the manipulators, which act on the solid body joints. Here, a micro lens array and a spatial filter array are specified as examples of the mounted optical components.
In order to permit these adjustments, firstly the inner mount part is arranged such that it can be displaced and fixed in the outer mount part in a plane perpendicular to an optical axis by means of actuating screws. Secondly, the inner mount frame of the outer mount part and the outer mount frame of the inner mount part are connected to each other via a detachable clamping device acting axially in a force-fitting manner. As a result, when the clamping device is released and the actuating screws are fixed, which means tightened, the two optical components can be adjusted in relation to each other by means of manipulation of the outer mount part and of the inner mount part or else only by means of manipulation of one of the two mount parts.
When the clamping device is fixed, which means acting axially in a force-fitting manner and clamping the inner mount part to the outer mount part, and with the actuating screws released, further, more precise adjustment of the two optical components in relation to each other is possible by means of manipulation of the inner mount part and an adjustment of both optical components relative to the reference base by means of manipulation of the outer mount part.
The drawback with this mount assembly is that, during the adjustment, the movement that is initiated has both translational and rotational components, which makes relatively long experimentation necessary.